Thermostat with heat and/or cool fan delays controlled by thermostat output

ABSTRACT

A thermostat includes within its circuitry a delay signal generator for delaying the activation and deactivation of an air circulation fan for a predetermined time period after which a heater or compressor is activated or deactivated.

BACKGROUND OF THE INVENTION

This invention relates generally to thermostats and, more particularly,to a thermostat method and apparatus for introducing delays in theenergizing and de-energizing of an air circulating fan of a forced aircomfort system.

In a forced air comfort system that may include a furnace and/or an airconditioner, an electrically driven air circulation fan is used to movethe conditioned air to the space for which the air being conditioned. Inolder furnaces and air conditioning systems, and in lower end systemsbeing manufactured today, the air circulating fan is energized andde-energized at the same time that the furnace heater or the airconditioning system compressor is energized or de-energized. Thisresults in the circulation of air that is not properly conditioned or tothe non-circulation of air that is properly conditioned. That is, in thecase of a furnace, non-heated or inadequately heated air is circulatedat start up, and when the furnace shuts down, the air that has beenheated is not circulated, thereby causing inefficiencies. Similarly, foran air conditioning system, warm unconditioned air is circulated at thebeginning of a cycle, and cool conditioned air is not circulated at theend of the cycle.

In high end furnaces and air conditioners of today, it is common toinclude control features within the system control board to introducedelays in the turning on and off of the circulating fan so as toovercome the problems discussed hereinabove. However, these features arenot available in older furnaces/air conditioners or low end furnaces/airconditioners. Accordingly, in order to obtain these features it ispresently necessary to purchase a new system.

Further, even in those systems where the delay functions can be includedin the system control apparatus, the delays will be set according togeneralized time periods which may not be appropriate for the particularinstallation and would not be adjustable to other times except possiblyby a service person who would need to make the individual changes ineach of the cooling and heating systems.

It is therefore an object of the present invention to provide animproved forced air comfort system control apparatus and method.

Another object of the present invention is the provision in a forced aircomfort system for greater comfort and efficiency in older and/or lessexpensive furnace/air conditioning systems.

Yet another object of the present invention is the provision in suchforced air comfort systems for initiating delays in the turning on andoff of the air circulation fan without upgrading the furnace/airconditioning system.

Another object of the present invention is the provision for a homeownerto easily adjust delay times to either or both of the heating andcooling systems by adjusting a single thermostat to meet the needs of aparticular system as installed.

Still another object of the present invention is the provision in aforced air comfort system for a thermostat which is economical tomanufacture and effective and efficient in use.

These objects and other features and advantages become more readilyapparent upon reference to the following descriptions when taken inconjunction with the appended drawings.

SUMMARY OF THE INVENTION

Briefly, in accordance with one aspect of the invention, a thermostatincludes within its internal control features, signal generating meansfor introducing a delay between the time in which a signal is sent toturn on the heater or compressor of a comfort system and the time inwhich the associated air circulation fan is turned on or off. In thisway, greater comfort and efficiencies are obtained without the need forupgrading the furnace/air conditioner.

In the drawings as hereinafter described, a preferred embodiment isdepicted; however various other modifications and alternateconstructions can be made thereto without departing from the true spritand scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a furnace and air conditionerinstallation into which the present invention has been incorporated.

FIG. 2 is a wiring diagram showing the thermostat as it is connected tothe furnace and the air conditioner.

FIG. 3 is a timing diagram of the various thermostat signals for turningon and off the components of the furnace and air conditioner inaccordance with the present invention.

FIG. 4 is a flow chart showing the function of the thermostat inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown a plan view of an enclosure 10with an installed furnace 11 and air conditioner or heat pump 12. Thefurnace 11 is mounted such that cold air from the enclosure is receivedby the furnace through cold air return 13 and thereafter hot air fromthe furnace is supplied to the enclosure 10 through supply ducts 14 andhot/cold air supply duct 16 to the enclosure 10. The furnace has ablower 17 for circulating the air from the enclosure through the coldair return 13 to the furnace 11 and through the furnace heat exchangers18, through supply duct 14 and back to the enclosure through hot/coldair supply duct 16.

The air conditioner or heat pump 12 is mounted such that the indoor coil19 is contained within supply duct 14 in communication with theenclosure air being circulated by the furnace blower, and that theoutdoor coil 21 is mounted outside the enclosure in communication withthe ambient air 22. The indoor coil 19 and the outdoor coil 21 areconnected through a reversing valve 23 to a compressor 24. The outdoorfan 26 is powered by an outdoor fan motor 27 located such that theambient air is circulated through the outdoor coil 21.

A control box 28 is arranged to control by way of signals on line 30from a thermostat 29, the furnace blower motor 15 by way of line 31, theheater or gas ignition system 20 by way of line 32, the compressor 24 byway of line 33, and the outdoor fan motor 27 by way of line 34,respectively. An outdoor temperature sensor 36 can also be provided forsensing the temperature and sending it to the control box 28 by line 37and then to the thermostat 29 by line 30.

Referring now to FIG. 2, the thermostat 29, the furnace 11 and the airconditioning system 12 are shown by their respective blocks with thevarious electrical interconnections being shown between the three units.For simplicity, the interconnections of the control board 28 are notshown since the signals to and from the thermostat 28 are designed tocommunicate directly with the components of the furnace 11 and the airconditioning system 12.

As will be seen, the W terminal of the thermostat 28 is intended toprovide signals to the W terminal of the furnace 11 so as to selectivelyactivate and deactivate the heater or gas ignition system 20. Similarly,the G terminal of the thermostat 29 is intended to communicate with theG terminal of the furnace 11 to selectively activate and deactivate theblower motor 15.

When the system is operating in the air conditioning or heat pump mode,the thermostat 29 communicates with the air conditioning by way of therespective Y terminals in order to activate and deactivate thecompressor 24 as shown. The cooled air is circulated, of course, by theblower 17, and thus the blower motor 15 is again activated by way ofcommunication between the respective G terminals as shown.

The R and C terminals of the respective thermostat 29, furnace 11 andair conditioner 12 are used for various 24 volt input control signalssuch as are used to operate the reversing valve 23, for example.

Referring now to FIG. 3, the various delay features of the signals fromthe thermostat 29 are shown.

As will be seen, for normal operation of the thermostat, the signals forturning on and off the heater and the fan in the case heating operation,and for turning on and off the air conditioner and fan in the case ofcooling, both occur at the same time.

With the present invention, however, a fan delay is introduced, suchthat at time T₁, the thermostat 29 provides a signal from its W terminalfor the furnace heater to turn on. At time T2, the thermostat 29provides a signal from its G terminal for the fan 25 to be turned on.The on-delay time of T2-T₁ is thus provided for the furnace heatexchangers to be heated up prior to the fan being turned on such thatcold air is not caused to be circulated into the enclosure 10, butrather, the fan comes on only after the furnace heat exchangers havebeen heated up to a satisfactory temperature.

When the thermostat receives an indication that the temperature of theenclosure 10 has been heated to a predetermined level, the furnace isthen turned off. A similar delay is provided at this time in order toallow the fan to continue to operate after the furnace heater 18 hasbeen shut off in order to obtain the benefit of the residual heat in theheat exchangers. That is, the heater is turned off at time T3 and theblower motor 15 is turned off at a later time, T₄. The off delay time ofT4-T3 allows for the economical distribution of heat within the heatexchanger that might otherwise be lost.

In a similar manner, the air conditioner compressor 24 is activated anddeactivated by signals from the Y terminal of the thermostat 29 at timesT₅ and T₇ as shown. Again, the signals to the fan motor 15, as receivedfrom terminal G of the thermostat 29 cause the fan to turn on at time T₆and turn off at time T₈ to provide a similar on-delay of time T₆-T₅ andan off-delay of time T₈-T₇. The on-delay allows for the air conditioningsystem to be operational for a sufficient time such that when the blowermotor 15 comes on, it is cooled air rather then hot air that iscirculated. Similarly, the off-delay allows for the continuedcirculation of the residual cool air in the system after the airconditioner is turned off at time T₇.

Referring now to FIG. 4, a flow chart of the present system is shownduring the heating operation wherein a demand signal is generated atstep 38 as determined by the difference between the said point of thethermostat and the actual temperature as indicated by the thermostat. Ifthe demand is greater than the specified off set as established by theoperator and set into the thermostat, then the heat is turned on asshown in steps 39 and 41.

If the on-delay timer is set in step 42 as discussed hereinabove, thenthe system will wait for the on-delay time, after which is will turn onthe fan in step 43.

When the demand is finally determined to be zero in step 44, the heaterwill be turned off at step 46. Again, if the off-delay timer is set instep 47, then the system will wait until the off-delay time has expired,after which the fan will be turned at step 48.

In the case of cooling operation, the on and off delay times willoperate in substantially the same way as described hereinabove.

1. A thermostat for energizing and de-energizing a forced air comfort system having a furnace and/or air conditioning system with a respective heater or compressor and an air circulating fan comprising: means within said thermostat for receiving a demand signal and for responsively generating a first signal for energizing said heater or compressor; means within said thermostat for generating a delay signal of a predetermined time period; and means within said thermostat for generating a second signal for energizing said circulation fan upon the passing of said predetermined time period following the energizing of said heater or compressor.
 2. A thermostat as set forth in claim 1 and further comprising: means within said thermostat for generating a third signal for de-energizing said heater or compressor; means within said thermostat for generating a off-delay signal of a predetermined time period; and means within said thermostat for generating a fourth signal for de-energizing said circulation fan upon the passing of said predetermined time-off period following the de-energizing of said heater or compressor.
 3. A method of operating a forced air comfort system having a furnace and/or air conditioner system with a respective heater or compressor and an air circulation fan all of which are turned on and off by signals from the thermostat, comprising the steps of: sensing a need for heating or cooling and sending a corresponding demand signal to said thermostat; responsively generating within said thermostat a first energizing signal for energizing said heater or compressor; in response to said energizing signal, generating within said thermostat an energizing delay signal of a desired time-on period; waiting for said desired time-on period following the energization of said heater or compressor; and generating within said thermostat a second energizing signal for responsively energizing said air circulation fan.
 4. A method as set forth in claim 3 and including the further steps of generating within said thermostat a first de-energizing signal for de-energizing said heater or compressor; in response to said de-energizing signal, generating within said thermostat a de-energizing delay signal of a desired time-off period; waiting for said desired time-off period following the de-energizing of said heater or compressor; and generating within said thermostat a second de-energizing signal for responsively de-energizing said air circulation fan.
 5. A thermostat for energizing and de-energizing a forced air comfort system having a furnace and/or air conditioning system with a respective heater or compressor and an air circulating fan comprising: a first signal generator for generating a delay signal which causes the air circulation fan to be activated only after a predetermined time period following the energization of the heater or compressor.
 6. A thermostat as set forth in claim 5 including a second signal generator for generating an off delay signal which causes the air circulation fan to be deactivated only after a predetermined time period following the de-energization of the heater of compressor.
 7. A thermostat as set forth in claim 1 wherein said forced air comfort system is a furnace and said circulation fan is turned on a predetermined time after said heater is energized.
 8. A thermostat as set forth in claim 1 wherein said forced air comfort system is an air conditioner and said circulation fan is turned on a predetermined time after said compression is energized. 